#include<bits/stdc++.h>
using namespace std;
const int maxn=5e6+5;
int t,m;
struct node{
	int value;
	int timee;
}a[maxn];
int dp[maxn];
int maxx,bian;
bool cmp(node a,node b){
	return a.timee<b.timee;
}
int main(){
	cin>>t>>m;
	for(int i=1;i<=m;i++){
		int helpt,helpv; cin>>helpt>>helpv;
		if(helpt<=t){
			++bian;
			a[bian].timee=helpt;
			a[bian].value=helpv;
		}
	}
	sort(a+1,a+1+bian,cmp);
	for(int i=bian;i>=1;i--){
		int j=1;
		while(t-a[i].timee<=a[j].timee){
			dp[i]=max(dp[i],dp[j]+a[j].value);
			j++;
		}
		maxx=max(maxx,dp[i]);
	}
	cout<<maxx<<endl;
	return 0;
}